Calibrated in-vacuum quantum efficiency system for metallic and III-V thin-film photocathodes

Abstract

The construction and calibration of a high vacuum system for thin film growth and in situ quantum efficiency (QE) measurement are described. Surface cleaning by in situ argon ion sputtering and annealing is supported. The QE measurement is based on an external 265 nm LED and in situ positively biased collector grid. The system is applied to two metallic and two semiconducting photocathodes: polycrystalline silver and copper, and single crystal InP and InSb. Surface cleaning protocols are shown to have a dramatic effect on the QE for all of these materials. The maximum QE values achieved for clean InSb and InP are around 8 × 10−5, for Cu 9 × 10−5 and for Ag 2 × 10−4.

Towards dark current suppression in metallic photocathodes by selected-area oxidation

“…This is consistent with a reduced oxide thickness (some oxide could reform during transfer through air to the QE vacuum system) and work function for the acetic acid-treated surface. The typical absolute QE for chemically treated Cu surfaces is 7 10 −5 [ 12 ]. No photocurrent could be measured for the two oxidised samples, i.e.…”

“…The quantum efficiency (QE) measurement system [ 12 ] was situated in a high vacuum stainless steel chamber with a base pressure of 10 −7 mbar. Photoemission is induced by a 265 nm UV LED (Roithner LaserTechnik GmbH), with a max radiated power of 0.5 mW and a spectral width of 13 nm.…”